1 /* 2 * Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_GC_G1_G1HEAPSIZINGPOLICY_HPP 26 #define SHARE_GC_G1_G1HEAPSIZINGPOLICY_HPP 27 28 #include "memory/allocation.hpp" 29 #include "utilities/numberSeq.hpp" 30 31 class G1Analytics; 32 class G1CollectedHeap; 33 34 // 35 // Contains heuristics for heap sizing, i.e. expansion or shrinking, during operation 36 // based on gc time ratio. 37 // 38 // The heuristics tracks both short term and long term behavior to effect heap 39 // size change. 40 // 41 // Short term tracking is based on short-term gc time ratio behavior: for this we 42 // record events for when actual gc time ratio is outside the range of 43 // [GCTimeRatio * G1MinimumPercentOfGCTimeRatio, GCTimeRatio] or not in a counter. 44 // If below that range, we decrement that counter, if above, we increment it. 45 // 46 // The intent of this mechanism is to filter short term events as heap sizing has 47 // some overhead. 48 // 49 // If that counter reaches the MinOverThresholdForExpansion we consider expansion, 50 // if that counter reaches -MinOverThresholdForShrink we consider heap shrinking. 51 // 52 // While doing so, we accumulate the difference to the midpoint of this range to 53 // guide the expansion/shrinking amount. 54 // 55 // Further, if there is no short-term based resizing event for a "long" time, we 56 // decay that counter, i.e. drop it towards zero again to avoid that previous 57 // intermediate length short term behavior followed by a quiet time and a single 58 // short term event causes unnecessary resizes. 59 // 60 // Long term behavior is solely managed by regularly comparing actual long term 61 // gc time ratio with the boundaries of above range in regular long term 62 // intervals. If current long term gc time ratio is outside, expand or shrink 63 // respectively. 64 // 65 class G1HeapSizingPolicy: public CHeapObj<mtGC> { 66 // MinOverThresholdForExpansion/Shrink define the number of actual gc time 67 // ratios over the upper and lower thresholds respectively. 68 const static int MinOverThresholdForExpansion = 4; 69 const static int MinOverThresholdForShrink = 4; 70 71 const G1CollectedHeap* _g1h; 72 const G1Analytics* _analytics; 73 74 const uint _long_term_interval; 75 // Number of times actual gc time ratio crossed lower and upper threshold 76 // recently; every time the upper threshold is exceeded, it is incremented, 77 // and decremented if the lower threshold is undercut. 78 int _ratio_exceeds_threshold; 79 // Recent actual gc time ratios relative to the middle of lower and upper threshold. 80 TruncatedSeq _recent_pause_ratios; 81 uint _long_term_count; 82 83 // Clear ratio tracking data used by resize_amount(). 84 void reset_ratio_tracking_data(); 85 void decay_ratio_tracking_data(); 86 87 // Scale "full" gc time ratio threshold with heap size as we want to resize more 88 // eagerly at small heap sizes. 89 double scale_with_heap(double pause_time_threshold); 90 91 // Scale the ratio delta depending on how far it exceeds the actual target gc time 92 // ratio. 93 double scale_resize_ratio_delta(double ratio_delta); 94 95 G1HeapSizingPolicy(const G1CollectedHeap* g1h, const G1Analytics* analytics); 96 public: 97 98 // Return by how many bytes the heap should be changed based on recent gc time 99 // ratio after young collection. Positive values mean expansion is desired, and 100 // negative values mean desired shrinking. 101 ssize_t resize_amount_after_young_gc(); 102 103 // Calculate the target capacity based on used bytes and free ratio. 104 size_t target_heap_capacity(size_t used_bytes, uintx free_ratio) const; 105 106 static G1HeapSizingPolicy* create(const G1CollectedHeap* g1h, const G1Analytics* analytics); 107 }; 108 109 #endif // SHARE_GC_G1_G1HEAPSIZINGPOLICY_HPP